The present invention relates to an internal combustion engine control system for controlling an internal combustion engine and, more particularly, to an internal combustion engine control system for controlling intake air and fuel in an internal combustion engine.
Generally, the timing of operations of the intake valve and the exhaust valve of engines including direct fuel injection engines is dependent only on the cam profiles of cams driven for rotation in synchronism with the rotation of the crankshaft of the engine. Accordingly, it is difficult to achieve optimum valve timing control in a wide range of operating condition. It is desirable to vary valve timing according to the operating condition to improve the output performance of the engine and the like. It is necessary to vary valve timing so that valve overlap period, i.e., a period in which both the intake and the exhaust valve are open, decreases to prevent the blowby of new charge while the engine is operating at a relatively low engine speed, and so that valve overlap period increases to supply new charge at a high charging efficiency by using exhaust gas pulsation while the engine is operating at a relatively high engine speed.
A technique relating to such a mode of control of valve timing is disclosed in JP-A No. 6-101508. This prior art technique controls negative pressure in the intake pipe minutely at an optimum value, and controls the timing of closing the intake valve on the basis of parameters indicating the operating condition of the engine including cooling water temperature, intake air temperature and time-dependent changes in the engine in addition to a map showing a function of engine speed and load to reduce pumping loss.
In an engine which is provided with a throttle valve disposed before an intake system to regulate the quantity of intake air and which regulates the quantity of fuel to be injected according to the quantity of intake air, the pressure in the intake pipe is lower than the atmospheric pressure in an operating range in which the load on the engine is relatively low, energy necessary for lowering the piston, i.e., energy necessary to achieve a suction stroke (pumping loss) increases, the ratio of pumping loss to engine output increases and fuel consumption increases.
The prior art technique, however, keeps the lift of the intake valve and the opening angle fixed and does not control the same. Therefore, the quantity of intake air to be sucked into the combustion chamber of the engine must be controlled by a throttle valve or the like disposed above the intake valve. Therefore, a negative pressure prevails in the intake passage below the throttle valve and in the combustion chamber, causing pumping loss. Accordingly, this prior art technique is not fully satisfactory as regards the reduction of pumping loss and fuel consumption.
In a direct fuel injection engine in which the fuel is injected directly into the combustion chamber, fuel injection timing is set so that the fuel is injected in a period during the suction stroke and the compression stroke in which the exhaust valve is closed to avoid discharging the unburned fuel. Consequently, time available for the evaporation of the fuel, i.e., time from fuel injection to ignition, is short. Therefore, the fuel must be injected through a fuel injector in small particles to promote the evaporation of the fuel and the mixing of the fuel with air. As is generally known, the higher the fuel injection pressure, the smaller is the particle size of the fuel. Therefore, the fuel is pressurized at a very high pressure of about 5 Mpa. However, the fuel injected at a high injection pressure has a very high spray penetration, impinges on the inner surface of the cylinder and the top of the piston, and part of the fuel adheres to the inner surface of the cylinder. The fuel adhering to the inner surface of the cylinder is exhausted without burning to increase the HC (hydrocarbon) content of the exhaust gas. The fuel injector for the direct fuel injection engine is required to inject the fuel in fine particles and to reduce the spray penetration in order that the foregoing problems are solved.
It is an object of the present invention to provide an internal combustion engine control system for controlling an internal combustion engine, capable of greatly reducing pumping loss while the engine is operating in a low-load range, of reducing fuel consumption, and of enabling satisfactory combustion without adversely affecting exhaust performance.
The foregoing object has been achieved by an internal combustion engine control system according to one embodiment of the present invention for controlling an internal combustion engine, comprising: a fuel injection control apparatus for controlling fuel injection quantity to be injected by a fuel supply system for supplying fuel to the internal combustion engine, and fuel injection timing; and a variable valve control for continuously or gradually varying at least opening timing, closing timing or lift of a intake valve or an exhaust valve for sealing up a combustion chamber of the internal combustion engine; wherein the fuel injection control apparatus controls at least fuel injection quantity or fuel injection timing on the basis of a value of a controlled variable provided by the variable valve control.
The foregoing object can be achieved by an internal combustion engine control system according to another embodiment of the present invention for controlling an internal combustion engine, comprising: a fuel injection control apparatus for controlling fuel injection quantity to be injected by a fuel injection system for directly injecting the fuel into a combustion chamber of the internal combustion engine, and fuel injection timing; and a variable valve control for continuously or gradually varying at least opening timing, closing timing or lift of a intake valve or an exhaust valve for sealing up the combustion chamber of the internal combustion engine; wherein the fuel injection control apparatus controls at least fuel injection quantity or fuel injection timing on the basis of a value of a controlled variable provided by the variable valve control.
The controller of the foregoing construction exercises the following actions and effects. The variable valve control regulates the opening timing, the closing timing and the lift of the intake valve and the exhaust valve to reduce pumping loss and fuel consumption while the engine is operating in a low-load operation range. The variable valve control regulates the opening timing, the closing timing and the lift of the intake valve and the exhaust valve to increase charging efficiency and to enhance the output power of the engine while the engine is operating in a high-load operation range. The fuel injection control apparatus controls fuel injection quantity and fuel injection timing according to changes in the variable valve control to inject the fuel into the combustion chamber in satisfactory particles to enable stable combustion and to reduce the hydrocarbon concentration of the exhaust gas.